Embryology

• Morula


  A ball of identical cells
• Blastocyst


  A fluid-filled cavity formed from two different cell types
• Blastocyst implantation


  The blastocyst sticks to and invades the uterine lining and wall
• Endometrium


  The uterine lining
• Zona pellucida


  The structure that must disappear from around the blastocyst to enable implantation
• Bilaminar embryonic disc


  Formed from the epiblast (upper) & hypoblast (lower) layers; the amniotic cavity forms above epiblast
• Primary yolk sac


  Formed below the hypoblast
• Syncytium


  A tissue consisting of a large number of nuclei within a common cytoplasm
• Amniotic cavity


  Filled with fluid
• Nutrient supply


  At this early stage, the cells of the embryo get nutrient by diffusion
• Extraembryonic mesoderm


  An additional layer consisting of cells and extracellular matrix
• Extraembryonic coelom


  Cavities that form within the extraembryonic mesoderm and eventually join together to form a fluid filled sac around the entire embryo
• Placenta formation


  The tissue layers that will contribute to the formation of the placenta
• Connecting stalk


  The overall structure that the connecting stalk will become
• Structures that will form within the connecting stalk


  • ?
• Morula formation


  Repeated mitotic divisions (cleavage)
• Zona pellucida


  The tissue layer that initially surrounds the morula and must eventually break down
• The blastocyst is formed from two different cell types
• Epithelium


  The tissue layer the blastocyst must adhere to prior to implantation
• Bilaminar embryonic disc


  Formed from the epiblast and hypoblast layers, which are derived from the blastocyst
• Trophoblast


  The embryonic cellular mass that assists with the implantation of the embryo into the endometrium
• Amniotic cavity


  The fluid filled sac that sits above the bilaminar embryonic disc
• Primary yolk sac


  The fluid filled sac that sits below the bilaminar embryonic disc
• Extraembryonic mesoderm (mesenchyme)


  The tissue layer where the extracellular matrix forms
• Chorionic cavity


  The fluid filled sac that forms within the extraembryonic mesoderm layer, allowing the embryonic disc to expand
• Gastrulation


  The process where cells from the epiblast layer migrate downwards to form the three layered (trilaminar) embryonic disc
• Prochordal (prechordal) plate


  Sits within the region of the future mouth/pharynx
• Cloaca plate


  Sits within the region of the future cloaca
• Primitive streak


  A raised area of epiblast (future ectoderm) that extends from the cloaca to the primitive node
• Primitive groove


  An indentation in the centre of the primitive streak, marking the region where cells are rapidly migrating downwards
• Intraembryonic mesoderm


  The new middle cell layer formed by the migrating epiblast cells during gastrulation
• Notochord


  Forms within the mesoderm layer, creating a longitudinal axis in the embryo
• Primitive node and pit


  The structure from which the notochord grows
• The primitive pit and node should disappear, as if they don't it can lead to teratoma formation at the distal end of the vertebral column
• Embryonic disc derivatives


  • Lining of gut tube, respiratory system and urinary system (from endoderm)
  • Skin & neural tissue (from ectoderm)
  • Paraxial mesoderm (forms?)
  • Intermediate mesoderm (forms?)
  • Lateral plate mesoderm (forms?)
• Somites


  Segmented blocks of paraxial mesoderm that form along the notochord, which give rise to different tissues
• Neural tube


  Forms from the ectoderm layer
• Tissues formed from the intraembryonic mesoderm

  • Serous membranes
  • Somites
  • Renal
  • Gonad
• Gut tube epithelium


  Derived from the endoderm
• One cell thick epithelium

  Has properties like being thin and fragile, but critical for protection and function